The present invention relates to a semiconductor device, particularly to a technique effective in the application to metallization for the bonding of a semiconductor device of a structure wherein the back surface of a semiconductor element is fixed using a soldering material or the like, and also effective in the application to a method for manufacturing such a semiconductor device.
As a semiconductor device of the type wherein the back surface of a semiconductor element is fixed, there is known a chip carrier of a structure wherein a semiconductor chip is face-down-bonded directly to a circuit board through CCB (Controlled Collapse Bonding) bump electrodes formed on a main surface of the chip and then a cap is applied to the back surface of the chip in a closely contacted state to provide a seal.
In such a chip carrier, as described, for example, in Japanese Patent Laid-Open No. 310139/1988, a heat transfer portion is formed and a hermetic seal is made thereby between the back surface of the semiconductor chip and the cap, using a soldering material, e.g. solder, for radiating heat directly from the back surface of the chip. On the back surface of the semiconductor chip, there is formed a metallized layer by plating an Au film, a Cr film, a Cu film and an Au film successively from the chip back surface in order, to improve the wettability for solder.
The chip carrier is assembled using the flip chip bonding technique described in Japan Metal Society Proc. Vol. 23, No. 12 (1984), pp. 1004-1006. First, thin Cr/Cu/Au film electrodes (i.e. BLM layer) are formed on aluminum electrodes of a silicon wafer with a semiconductor integrated circuit formed thereon using a vapor evaporation technique, a fine processing technique, etc. Next, a metallized layer comprising Au/Cr/Cu/Au films is formed on the back of the Si wafer. Further, solder is fed onto the BLM layer and heat-melted in a nitrogen atmosphere (a wet back process) to form solder bumps, then the wafer is cut into individual chips. Thereafter, onto a circuit board with electrodes, etc. formed thereon there is bonded each semiconductor chip by face down bonding, that is, in such a manner that the circuit-formed main surface of the chip is opposed to the circuit board, followed by heat-melting (a mounting and reflow process) Subsequently, solder is fed to a back of the semiconductor chip and also to a sealing portion of the circuit board, and a cap is put on the back of the chip in a closely contacted state, followed by heat-melting, whereby the chip is hermetically sealed in the interior